Heat-assisted magnetic recording (HAMR) writers have been developed to meet the growing demand for improved magnetic disk drive data capacity. HAMR writers heat high-stability magnetic compounds to apply changes in magnetic orientation. These materials can store bits in a much smaller areas without being limited by the superparamagnetic effect. In this regard, HAMR writers are a promising solution for pushing the data areal density of a hard disk to 1 Tbit/in2 and beyond.
One of the critical components of the HAMR is the Near-Field Transducer (NFT) which comprises an NFT pin and an NFT main body. The NFT focuses incoming light to a nano-sized highly concentrated optical spot and delivers enough energy through the NFT pin to the media to achieve HAMR writing. The NFT couples the light from a waveguide (WG) to a resonator (the main body portion), where the light wave excites a surface plasmon wave and becomes resonant. A node of the resonant light wave is aligned with the pin by turning the polarization of the NFT, for example, by adjusting two arms of the waveguide.
FIG. 1 illustrates the temperature distribution within the conventional NFT 100. A quadruple pole resonance is observed. Because the pin 101 takes the role to focus the resonant wave energy, it is the highest temperature component of the already hot NFT 100. In the conventional NFT 100, the temperature difference between the NFT pin 101 and NFT main body 102 can be as high as 100 K. The conventional NFT comprises a noble metal or metal alloy in the resonator portion (main body) 102 and pin portion 101. Generally, gold (Au) or silver (Ag) are used. A noble metal is one of the few known options for achieving optical resonance in the visible light range. However, noble metals such as gold have a high thermal conductivity. The very high temperature of the conventional NFT noble metal pin 101, in addition to reducing its life span, causes other problems.
As illustrated in FIG. 2, the conventional NFT pin 101 significantly protrudes because of the high mismatch between the coefficient of thermal expansion (CTE) of the pin 101 and the surrounding cladding material. The conventional NFT pin with Au-pin and SiO2 cladding material, for example, typically has a CTE of 14.2 ppm/K for the Au pin and a CTE of 0.8 ppm/K for the surrounding SiO2 cladding material. Scanning electron microscope (SEM) image 200 illustrates one example view of the protrusion. Atomic force microscope (AFM) image 210 illustrates another view of the protrusion. This protrusion can be as high as 10 nm. The protruding pin may break the thin layer of carbon overcoat (˜1-2 nm) on the ABS plane protecting the slider. This leads to burnishing of the magnetic writer against the media and significantly shortens the pin's lifespan. Eventually, the head-disk-interface is spoiled, and the driver loses function. Accordingly, it is desirable to manufacture an HAMR with NFT that does not exhibit this property.